29s P rocedures in Refraction Siagrajp. Construction. - For a chosen 

 shore location hvTJ-rogrppliic charts shovxing bottom topography of the area ajre 

 obtained^. Two or raore chsxts may be necessary, of differing scale, but tb£ 

 procedures are identical, for charts of snj scale* Next, underwater contours 

 are drawn on the chart, or on a tracing paper overlay, for various depths, 

 depending on the diagr'-m accuracy desired. If overlays are used (this will 

 preserve the charts) the shore line should be traced in for reference = In 

 tracing the contours, judgment must be used in "smoothing out" small irregularities, 

 since bottom features xfhich are coiriparatively small in respect to the wave 

 length do not .affect the wave appreciabl3/-, 



30., The range of wave periods to be used is determined hj a hindcast- 

 ing study of historical weather charts or from otter historical data re- 

 lating to wave periods^ With the wave period so determined, '^-lA'p values 

 for each contour interval should be marked between the contours , The 

 method of corputing 0^ /O is illustrated by Table 2. A tabulation of C-,/Gp 



and C /C- , for various contour intervals and T-mve periods is given in 



Table 8 of i\ppendix D» 



Table 2 - CoiTiputations for values of C- i/Cp ,- T = 10 sec . 



















d 



d 



d 

 Lo 



taaih2Trd 

 L 



5.12 T^ 



c 



^l/'^2 or 



^2/°! 



(1) 



(2) 



(3) 



(U) 



(5) 



(6) 



(7) 



(7) 



(fathom) 



feet 















1 







0.-0117 



0.26 



512 



133 



1,L.2 



O.70I1 



2 



12 



0.0235 



0.37 



512 



189 



1»22 



0«82 



3 



18 



0.0352 



0,1(5 



512 



230 



1.16 



0^87 



It 



21; 



0, Oil 69 



0.52 



512 



266 







Columns 1 and 2 are depths corresponding to each chart contour. 

 These would extend from 1 fathom to a depth equal to L /2. 



Column 3 is column 2 divided by L corresponding to the determined 

 period =. 



Column h°, these values may be found in Table 1 of JSppendix D, as a 



function of d/L .. 

 ' o 



Column 6 is the product of colmiins k and 5« 

 Column 7 is the quotient of successive terms in column 6.^<: 



21 



